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Honors & Awards

  • T32 HIV, AIDS and Opportunistic Infections, National Institute of Allergy and Infectious Diseases Extramural Activities (2014-2017)

Professional Education

  • Ph.D., Albert Einstein College of Medicine, Biomedical Sciences (2019)
  • M.S., Albert Einstein College of Medicine, Biomedical Sciences (2015)
  • M.S., University of Alaska, Anchorage, Biological Sciences (2013)
  • B.S., University of Alaska, Anchorage, Biological Sciences (2010)

Stanford Advisors


All Publications

  • Cyclophilin A Prevents HIV-1 Restriction in Lymphocytes by Blocking Human TRIM5? Binding to the Viral Core. Cell reports Selyutina, A. n., Persaud, M. n., Simons, L. M., Bulnes-Ramos, A. n., Buffone, C. n., Martinez-Lopez, A. n., Scoca, V. n., Di Nunzio, F. n., Hiatt, J. n., Marson, A. n., Krogan, N. J., Hultquist, J. F., Diaz-Griffero, F. n. 2020; 30 (11): 3766?77.e6


    Disruption of cyclophilin A (CypA)-capsid interactions affects HIV-1 replication in human lymphocytes. To understand this mechanism, we utilize human Jurkat cells, peripheral blood mononuclear cells (PBMCs), and CD4+ Tácells. Our results show that inhibition of HIV-1 infection caused by disrupting CypA-capsid interactions is dependent on human tripartite motif 5? (TRIM5?hu), showing that TRIM5?hu restricts HIV-1 in CD4+ Tácells. Accordingly, depletion of TRIM5?hu in CD4+ Tácells rescues HIV-1 that fail to interact with CypA, such as HIV-1-P90A. We found that TRIM5?hu binds to the HIV-1 core. Disruption of CypA-capsid interactions fail to affect HIV-1-A92E/G94D infection, correlating with the loss of TRIM5?hu binding to HIV-1-A92E/G94D cores. Disruption of CypA-capsid interactions in primary cells has a greater inhibitory effect on HIV-1 when compared to Jurkat cells. Consistent with TRIM5? restriction, disruption of CypA-capsid interactions in CD4+ Tácells inhibits reverse transcription. Overall, our results reveal that CypA binding to the core protects HIV-1 from TRIM5?hu restriction.

    View details for DOI 10.1016/j.celrep.2020.02.100

    View details for PubMedID 32187548

  • Proinflammatory IgG Fc structures in patients with severe COVID-19 Nature Immunology Chakraborty, S., Gonzales, J., Edwards, K., Mallajosyulla, V., Buzzanco, A. S., Sherwood, R., Buffone, C., Kathale, N., Providenza, S., Xie, M. M., Andrews, J. R., Blish, C. A., Singh, U., Dugan, H., Wilson, P. C., Pham, T. D., Boyd, S. D., Nadeau, K. C., Pinsky, B. A., Zhang, S., Memoli, M. J., Taubenberger, J. K., Morales, T., Schapiro, J. M., Tan, G. S., et al 2020
  • The ability of SAMHD1 to block HIV-1 but not SIV requires expression of MxB VIROLOGY Buffone, C., Kutzner, J., Opp, S., Martinez-Lopez, A., Selyutina, A., Coggings, S., Studdard, L. R., Ding, L., Kim, B., Spearman, P., Schaller, T., Diaz-Griffero, F. 2019; 531: 260?68


    SAMHD1 is a human restriction factor known to prevent infection of macrophages, resting CD4+ T cells, and dendritic cells by HIV-1. To test the contribution of MxB to the ability of SAMHD1 to block HIV-1 infection, we created human THP-1 cell lines that were knocked out for expression of MxB, SAMHD1, or both. Interestingly, MxB depletion renders SAMHD1 ineffective against HIV-1 but not SIVmac. We observed similar results in human primary macrophages that were knockdown for the expression of MxB. To understand how MxB assists SAMHD1 restriction of HIV-1, we examined direct interaction between SAMHD1 and MxB in pull-down experiments. In addition, we investigated several properties of SAMHD1 in the absence of MxB expression, including subcellular localization, phosphorylation of the SAMHD1 residue T592, and dNTPs levels. These experiments showed that SAMHD1 restriction of HIV-1 requires expression of MxB.

    View details for DOI 10.1016/j.virol.2019.03.018

    View details for Web of Science ID 000466822000025

    View details for PubMedID 30959264

    View details for PubMedCentralID PMC6487861

  • Nup153 Unlocks the Nuclear Pore Complex for HIV-1 Nuclear Translocation in Nondividing Cells JOURNAL OF VIROLOGY Buffone, C., Martinez-Lopez, A., Fricke, T., Opp, S., Severgnini, M., Cifola, I., Petiti, L., Frabetti, S., Skorupka, K., Zadrozny, K. K., Ganser-Pornillos, B. K., Pornillos, O., Di Nunzio, F., Diaz-Griffero, F. 2018; 92 (19)


    Human immunodeficiency virus type 1 (HIV-1) displays the unique ability to infect nondividing cells. The capsid of HIV-1 is the viral determinant for viral nuclear import. To understand the cellular factors involved in the ability of HIV-1 to infect nondividing cells, we sought to find capsid mutations that allow the virus to infect dividing but not nondividing cells. Because the interaction of capsid with the nucleoporin protein 153 (Nup153) is important for nuclear import of HIV-1, we solved new crystal structures of hexameric HIV-1 capsid in complex with a Nup153-derived peptide containing a phenylalanine-glycine repeat (FG repeat), which we used to guide structure-based mutagenesis of the capsid-binding interface. HIV-1 viruses with mutations in these capsid residues were tested for their ability to infect dividing and nondividing cells. HIV-1 viruses with capsid N57 substitutions infected dividing but not nondividing cells. Interestingly, HIV-1 viruses with N57 mutations underwent reverse transcription but not nuclear translocation. The mutant capsids also lost the ability to interact with Nup153 and CPSF6. The use of small molecules PF74 and BI-2 prevented the interaction of FG-containing nucleoporins (Nups), such as Nup153, with the HIV-1 core. Analysis of integration sites in HIV-1 viruses with N57 mutations revealed diminished integration into transcriptionally active genes in a manner resembling that of HIV-1 in CPSF6 knockout cells or that of HIV-1-N74D. The integration pattern of the N57 mutant HIV-1 can be explained by loss of capsid interaction with CPSF6, whereas capsid interaction with Nup153 is required for HIV-1 to infect nondividing cells. Additionally, the observed viral integration profiles suggested that integration site selection is a multiparameter process that depends upon nuclear factors and the state of the cellular chromatin.IMPORTANCE One of the key advantages that distinguish lentiviruses, such as HIV-1, from all other retroviruses is its ability to infect nondividing cells. Interaction of the HIV-1 capsid with Nup153 and CPSF6 is important for nuclear entry and integration; however, the contribution of each of these proteins to nuclear import and integration is not clear. Using genetics, we demonstrated that these proteins contribute to different processes: Nup153 is essential for the HIV-1 nuclear import in nondividing cells, and CPSF6 is important for HIV-1 integration. In addition, nuclear factors such as CPSF6 and the state of the chromatin are known to be important for integration site selection; nevertheless, the preferential determinant influencing integration site selection is not known. This work demonstrates that integration site selection is a multiparameter process that depends upon nuclear factors and the state of the cellular chromatin.

    View details for DOI 10.1128/JVI.00648-18

    View details for Web of Science ID 000444430700003

    View details for PubMedID 29997211

    View details for PubMedCentralID PMC6146805

  • Functionality of Redox-Active Cysteines Is Required for Restriction of Retroviral Replication by SAMHD1 CELL REPORTS Wang, Z., Bhattacharya, A., White, T., Buffone, C., McCabe, A., Nguyen, L. A., Shepard, C. N., Pardo, S., Kim, B., Weintraub, S. T., Demeler, B., Diaz-Griffero, F., Ivanov, D. N. 2018; 24 (4): 815?23


    SAMHD1 is a dNTP triphosphohydrolase (dNTPase) that impairs retroviral replication in a subset of non-cycling immune cells. Here we show that SAMHD1 is a redox-sensitive enzyme and identify three redox-active cysteines within the protein: C341, C350, and C522. The three cysteines reside near one another and the allosteric nucleotide binding site. Mutations C341S and C522S abolish the ability of SAMHD1 to restrict HIV replication, whereas the C350S mutant remains restriction competent. The C522S mutation makes the protein resistant to inhibition by hydrogen peroxide but has no effect on theátetramerization-dependent dNTPase activity of SAMHD1 inávitro or on the ability of SAMHD1 to deplete cellular dNTPs. Our results reveal that enzymatic activation of SAMHD1 via nucleotide-dependent tetramerization is not sufficient for the establishment of the antiviral state and that retroviral restriction depends on the ability of the protein to undergo redox transformations.

    View details for DOI 10.1016/j.celrep.2018.06.090

    View details for Web of Science ID 000439589900004

    View details for PubMedID 30044979

    View details for PubMedCentralID PMC6067006

  • Infection by Zika viruses requires the transmembrane protein AXL, endocytosis and low pH VIROLOGY Persaud, M., Martinez-Lopez, A., Buffone, C., Porcelli, S. A., Diaz-Griffero, F. 2018; 518: 301?12


    The recent Zika virus (ZIKV) outbreak in Brazil has suggested associations of this virus infection with neurological disorders, including microcephaly in newborn infants and Guillian-BarrÚ?syndrome in adults. Previous reports have shown that AXL, a transmembrane receptor tyrosine kinase protein, is essential for ZIKV infection of mammalian cells, but this remains controversial. Here, we have assessed the involvement of AXL in the ability of ZIKV to infect mammalian cells, and also the requirement for endocytosis and acidic pH. We demonstrated that AXL is essential for ZIKV infection of human fibroblast cell line HT1080 as the targeted deletion of the gene for AXL in HT1080 cells made them no longer susceptible to ZIKV infection. Our results also showed that infection was prevented by lysosomotropic agents such as ammonium chloride, chloroquine and bafilomycin A1, which neutralize the normally acidic pH of endosomal compartments. Infection by ZIKV was also blocked by chlorpromazine, indicating a requirement for clathrin-mediated endocytosis. Taken together, our findings suggest that AXL most likely serves as an attachment factor for ZIKV on the cell surface, and that productive infection requires endocytosis and delivery of the virus to acidified intracellular compartments.

    View details for DOI 10.1016/j.virol.2018.03.009

    View details for Web of Science ID 000431388000032

    View details for PubMedID 29574335

  • Effects of T592 phosphomimetic mutations on tetramer stability and dNTPase activity of SAMHD1 can not explain the retroviral restriction defect SCIENTIFIC REPORTS Bhattacharya, A., Wang, Z., White, T., Buffone, C., Nguyen, L. A., Shepard, C. N., Kim, B., Demeler, B., Diaz-Griffero, F., Ivanov, D. N. 2016; 6: 31353


    SAMHD1, a dNTP triphosphohydrolase, contributes to interferon signaling and restriction of retroviral replication. SAMHD1-mediated retroviral restriction is thought to result from the depletion of cellular dNTP pools, but it remains controversial whether the dNTPase activity of SAMHD1 is sufficient for restriction. The restriction ability of SAMHD1 is regulated in cells by phosphorylation on T592. Phosphomimetic mutations of T592 are not restriction competent, but appear intact in their ability to deplete cellular dNTPs. Here we use analytical ultracentrifugation, fluorescence polarization and NMR-based enzymatic assays to investigate the impact of phosphomimetic mutations on SAMHD1 tetramerization and dNTPase activity in vitro. We find that phosphomimetic mutations affect kinetics of tetramer assembly and disassembly, but their effects on tetramerization equilibrium and dNTPase activity are insignificant. In contrast, the Y146S/Y154S dimerization-defective mutant displays a severe dNTPase defect in vitro, but is indistinguishable from WT in its ability to deplete cellular dNTP pools and to restrict HIV replication. Our data suggest that the effect of T592 phosphorylation on SAMHD1 tetramerization is not likely to explain the retroviral restriction defect, and we hypothesize that enzymatic activity of SAMHD1 is subject to additional cellular regulatory mechanisms that have not yet been recapitulated in vitro.

    View details for DOI 10.1038/srep31353

    View details for Web of Science ID 000381183600002

    View details for PubMedID 27511536

    View details for PubMedCentralID PMC4980677

  • HIV-1 capsid is involved in post-nuclear entry steps RETROVIROLOGY Chen, N., Zhou, L., Gane, P. J., Opp, S., Ball, N. J., Nicastro, G., Zufferey, M., Buffone, C., Luban, J., Selwood, D., Diaz-Griffero, F., Taylor, I., Fassati, A. 2016; 13: 28


    HIV-1 capsid influences viral uncoating and nuclear import. Some capsid is detected in the nucleus but it is unclear if it has any function. We reported that the antibiotic Coumermycin-A1 (C-A1) inhibits HIV-1 integration and that a capsid mutation confers resistance to C-A1, suggesting that capsid might affect post-nuclear entry steps.Here we report that C-A1 inhibits HIV-1 integration in a capsid-dependent way. Using molecular docking, we identify an extended binding pocket delimited by two adjacent capsid monomers where C-A1 is predicted to bind. Isothermal titration calorimetry confirmed that C-A1 binds to hexameric capsid. Cyclosporine washout assays in Jurkat CD4+ T cells expressing engineered human TRIMCyp showed that C-A1 causes faster and greater escape from TRIMCyp restriction. Sub-cellular fractionation showed that small amounts of capsid accumulated in the nuclei of infected cells and C-A1 reduced the nuclear capsid. A105S and N74D capsid mutant viruses did not accumulate capsid in the nucleus, irrespective of C-A1 treatment. Depletion of Nup153, a nucleoporin located at the nuclear side of the nuclear pore that binds to HIV-1 capsid, made the virus less susceptible to TRIMCyp restriction, suggesting that Nup153 may help maintain some integrity of the viral core in the nucleus. Furthermore C-A1 increased binding of CPSF6, a nuclear protein, to capsid.Our results indicate that capsid is involved in post-nuclear entry steps preceding integration.

    View details for DOI 10.1186/s12977-016-0262-0

    View details for Web of Science ID 000374678300001

    View details for PubMedID 27107820

    View details for PubMedCentralID PMC4842275

  • Ebselen, a Small-Molecule Capsid Inhibitor of HIV-1 Replication ANTIMICROBIAL AGENTS AND CHEMOTHERAPY Thenin-Houssier, S., de Vera, I. S., Pedro-Rosa, L., Brady, A., Richard, A., Konnick, B., Opp, S., Buffone, C., Fuhrmann, J., Kota, S., Billack, B., Pietka-Ottlik, M., Tellinghuisen, T., Choe, H., Spicer, T., Scampavia, L., Diaz-Griffero, F., Kojetin, D. J., Valente, S. T. 2016; 60 (4): 2195?2208


    The human immunodeficiency virus type 1 (HIV-1) capsid plays crucial roles in HIV-1 replication and thus represents an excellent drug target. We developed a high-throughput screening method based on a time-resolved fluorescence resonance energy transfer (HTS-TR-FRET) assay, using the C-terminal domain (CTD) of HIV-1 capsid to identify inhibitors of capsid dimerization. This assay was used to screen a library of pharmacologically active compounds, composed of 1,280in vivo-active drugs, and identified ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one], an organoselenium compound, as an inhibitor of HIV-1 capsid CTD dimerization. Nuclear magnetic resonance (NMR) spectroscopic analysis confirmed the direct interaction of ebselen with the HIV-1 capsid CTD and dimer dissociation when ebselen is in 2-fold molar excess. Electrospray ionization mass spectrometry revealed that ebselen covalently binds the HIV-1 capsid CTD, likely via a selenylsulfide linkage with Cys198 and Cys218. This compound presents anti-HIV activity in single and multiple rounds of infection in permissive cell lines as well as in primary peripheral blood mononuclear cells. Ebselen inhibits early viral postentry events of the HIV-1 life cycle by impairing the incoming capsid uncoating process. This compound also blocks infection of other retroviruses, such as Moloney murine leukemia virus and simian immunodeficiency virus, but displays no inhibitory activity against hepatitis C and influenza viruses. This study reports the use of TR-FRET screening to successfully identify a novel capsid inhibitor, ebselen, validating HIV-1 capsid as a promising target for drug development.

    View details for DOI 10.1128/AAC.02574-15

    View details for Web of Science ID 000376496100029

    View details for PubMedID 26810656

    View details for PubMedCentralID PMC4808204

  • Restriction of HIV-1 Requires the N-Terminal Region of MxB as a Capsid-Binding Motif but Not as a Nuclear Localization Signal JOURNAL OF VIROLOGY Schulte, B., Buffone, C., Opp, S., Di Nunzio, F., Vieira, D., Brandariz-Nunez, A., Diaz-Griffero, F. 2015; 89 (16): 8599?8610


    The interferon alpha (IFN-?)-inducible restriction factor MxB blocks HIV-1 infection after reverse transcription but prior to integration. Fate-of-capsid experiments have correlated the ability of MxB to block HIV-1 infection with stabilization of viral cores during infection. We previously demonstrated that HIV-1 restriction by MxB requires capsid binding and oligomerization. Deletion and gain-of-function experiments have mapped the HIV-1 restriction ability of MxB to its N-terminal 25 amino acids. This report reveals that the N-terminal 25 amino acids of MxB exhibit two separate functions: (i) the ability of MxB to bind to HIV-1 capsid and (ii) the nuclear localization signal of MxB, which is important for the ability of MxB to shuttle into the nucleus. To understand whether MxB restriction of HIV-1 requires capsid binding and/or nuclear localization, we genetically separated these two functions and evaluated their contributions to restriction. Our experiments demonstrated that the (11)RRR(13) motif is important for the ability of MxB to bind capsid and to restrict HIV-1 infection. These experiments suggested that capsid binding is necessary for the ability of MxB to block HIV-1 infection. Separately from the capsid binding function of MxB, we found that residues (20)KY(21) regulate the ability of the N-terminal 25 amino acids of MxB to function as a nuclear localization signal; however, the ability of the N-terminal 25 amino acids to function as a nuclear localization signal was not required for restriction.MxB/Mx2 blocks HIV-1 infection in cells from the immune system. MxB blocks infection by preventing the uncoating process of HIV-1. The ability of MxB to block HIV-1 infection requires that MxB binds to the HIV-1 core by using its N-terminal domain. The present study shows that MxB uses residues (11)RRR(13) to bind to the HIV-1 core during infection and that these residues are required for the ability of MxB to block HIV-1 infection. We also found that residues (20)KY(21) constitute a nuclear localization signal that is not required for the ability of MxB to block HIV-1 infection.

    View details for DOI 10.1128/JVI.00753-15

    View details for Web of Science ID 000358278200042

    View details for PubMedID 26063425

    View details for PubMedCentralID PMC4524248

  • Contribution of MxB Oligomerization to HIV-1 Capsid Binding and Restriction JOURNAL OF VIROLOGY Buffone, C., Schulte, B., Opp, S., Diaz-Griffero, F. 2015; 89 (6): 3285?94


    The alpha interferon (IFN-?)-inducible restriction factor myxovirus B (MxB) blocks HIV-1 infection after reverse transcription but prior to integration. MxB binds to the HIV-1 core, which is composed of capsid protein, and this interaction leads to inhibition of the uncoating process of HIV-1. Previous studies suggested that HIV-1 restriction by MxB requires binding to capsid. This work tests the hypothesis that MxB oligomerization is important for the ability of MxB to bind to the HIV-1 core. For this purpose, we modeled the structure of MxB using the published tertiary structure of MxA. The modeled structure of MxB guided our mutagenic studies and led to the discovery of several MxB variants that lose the capacity to oligomerize. In agreement with our hypothesis, MxB variants that lost the oligomerization capacity also lost the ability to bind to the HIV-1 core. MxB variants deficient for oligomerization were not able to block HIV-1 infection. Overall, our work showed that oligomerization is required for the ability of MxB to bind to the HIV-1 core and block HIV-1 infection.MxB is a novel restriction factor that blocks infection of HIV-1. MxB is inducible by IFN-?, particularly in T cells. The current work studies the oligomerization determinants of MxB and carefully explores the contribution of oligomerization to capsid binding and restriction. This work takes advantage of the current structure of MxA and models the structure of MxB, which is used to guide structure-function studies. This work leads to the conclusion that MxB oligomerization is important for HIV-1 capsid binding and restriction.

    View details for DOI 10.1128/JVI.03730-14

    View details for Web of Science ID 000350208900024

    View details for PubMedID 25568212

    View details for PubMedCentralID PMC4337540

  • BI-2 destabilizes HIV-1 cores during infection and Prevents Binding of CPSF6 to the HIV-1 Capsid RETROVIROLOGY Fricke, T., Buffone, C., Opp, S., Valle-Casuso, J., Diaz-Griffero, F. 2014; 11: 120


    The recently discovered small-molecule BI-2 potently blocks HIV-1 infection. BI-2 binds to the N-terminal domain of HIV-1 capsid. BI-2 utilizes the same capsid pocket used by the small molecule PF74. Although both drugs bind to the same pocket, it has been proposed that BI-2 uses a different mechanism to block HIV-1 infection when compared to PF74.This work demonstrates that BI-2 destabilizes the HIV-1 core during infection, and prevents the binding of the cellular factor CPSF6 to the HIV-1 core.Overall this short-form paper suggests that BI-2 is using a similar mechanism to the one used by PF74 to block HIV-1 infection.

    View details for DOI 10.1186/s12977-014-0120-x

    View details for Web of Science ID 000346680600001

    View details for PubMedID 25496772

    View details for PubMedCentralID PMC4271331

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